1. Field of the Invention
This invention relates generally to apparatus for blasting, painting or otherwise treating the walls of large structures such as water towers, petroleum storage tanks, warehouses, factories, etc., and particularly to apparatus used to create a substantially sealed mobile work enclosure against the walls of such structures.
2. Description of the Prior Art
There is a growing consciousness regarding the environment and, in an attempt to protect the environment, the use and handling of certain materials is controlled.
Traditionally, blast cleaning operations were conducted in the open allowing the blast media and waste materials to become airborne and fall unheeded anywhere. Since the blast media is blown against the structure at high pressure, the blast media and waste material if not contained would fall over a large area and in high winds that area would be even larger. Such contamination is undesirable and accordingly many jurisdictions have imposed regulations to ensure that the blast media and waste materials are contained. Furthermore, some of the materials which are being removed are considered hazardous, such as lead-based paint, and it is therefore important to ensure that they are contained when removed.
In order to meet the requirements to contain the blast media and waste material, a number of systems have been proposed, including totally enclosing the structure, enclosed movable platforms, movable remote cleaning units, and hand-held vacuum blasters. These systems, however, are often difficult to use, costly and/or time-consuming to implement.
In prior art systems, in order to totally enclose a water tower, for example, a tarpaulin assembly has been used. The tarpaulin assembly includes a sock portion, a hat portion and supporting means. The supporting means includes a plurality of upper supports which are installed on the water tower, which is time-consuming. A plurality of supporting ropes are attached to the upper supports and the sock portion of the tarpaulin. The sock portion is then pulled up the side of the water tower. The hat portion of the tarpaulin which covers the top of the water tower is then attached to the sock portion. This tarpaulin assembly is very time-consuming and cumbersome to install and remove. It cannot be used in high winds since the wind load on the tarpaulin greatly increases the load on the water tower. Accordingly, in high winds the sock portion must be dropped and the work must be stopped even in only moderately high winds such as 20 miles per hour, so that there is enough time for the workers to get out and drop the sock before the wind increases further. Other problems include that it is difficult to maintain a sealed connection between the sock portion and the hat portion of the tarpaulin. Furthermore, the tarpaulin itself is costly and is susceptible to being ripped by high winds, as the tarpaulin is raised and lowered against guide wires.
Prior art movable platforms having enclosed platforms for use in cleaning buildings include those shown in U.S. Pat. No. 4,649,672 issued to Thomann on Mar. 17, 1987; U.S. Pat. No. 5,038,527 issued to Fastje on Aug. 21, 1990; and U.S. Pat. No. 4,949,512 issued to Thomann on Aug. 13, 1991.
Prior art remote-controlled units include for example the unit shown in U.S. Pat. No. 4,825,598 issued to Schlick on May 2, 1989. Such units are complex and intricate machines which are expensive to build and maintain and labor intensive to operate. Accordingly, they are expensive to operate.
The prior art hand-held vacuum blasters are mobile hand-held machines which both blast and contain the blast media. The nozzle of the blaster forms a seal against the structure so that no blast media or waste material can escape into the air. The hand-held vacuum blasters are particularly appropriate for spot blasting but they are too time-consuming to use for a large structure.
Other surface treatments, such as painting or chemical treatment, also may require an enclosed work area against the wall of the structure. Even where such an enclosure is not mandatory, it may be desirable for worker convenience and/or safety.
Accordingly there is a need for an apparatus which can be adapted to provide an enclosed work area against the walls of large structures. The apparatus should be readily adaptable to structures of different sizes and shapes, and should be relatively easy to install. It is also important that it be able to travel along or around the walls of the structure easily.